The present invention relates to a panel with an anti-reflective multi-layered film thereon.
Various types of an anti-reflective film consisting of a single or a plurality of layers have been proposed wherein the film is coated on the front surface of a display device such as a cathode ray tube or on a panel to be disposed in front of the display device in order to eliminate the difficulty that the display portion is hardly seen due to an image by the reflection of an external light, and to reduce a degree of reflection.
As the anti-reflective film, there have been proposed a single layered anti-reflective film wherein a material having a low refractive index is used to form a layer having an optical thickness of .lambda./4 of a wave length which causes reflection, a two-layered anti-reflective film wherein two layers of a low refractive index layer and a high refractive index layer are coated to have respective optical thickness of .lambda./4 and .lambda./2 when viewed from the side of air, a three-layered anti-reflective film wherein three layers of a low refractive index layer, a high refractive index layer and an intermediate refractive index layer are coated to have respective optical thickness of .lambda./4, .lambda./2 and .lambda./4 when viewed from the side of air, and a four anti-reflective film wherein four layers of a low refractive index layer, a high refractive index layer, an intermediate refractive index layer and a low refractive index layer to have respective optical thickness of .lambda./4, .lambda./2, .lambda./4 and .lambda./4 when viewed from the side of air.
On the other hand, glass or a plastic material used for a cathode ray tube or a front panel has no electric conducting property, and the surface of the cathode ray tube is electrified by an amount of static electricity produced during the operation of the cathode ray tube. The static electricity causes an electric discharge to a human body or is apt to attract dust. This causes a great problem in a terminal of a computer, a display device for a word processor, and so on.
Accordingly, there has been studied to propose an anti-reflective film having electric conductive property, namely, an anti-reflective film wherein at least one layer is composed of a transparent material having electric conductive property. There has been known as a transparent conductive film, ITO (tin-doped indium oxide), SnO.sub.2 (tin oxide) and so on. However, these materials have a high refractive index (for instance, ITO has a refractive index of about 2.0 and SnO.sub.2 has 1.90), and therefore the construction of film for the anti-reflective film is limited. Namely, since the transparent electric conductive layer has a high refractive index, it does not function as a single-layered anti-reflective film and rather, it enhances reflectivity. Further, in a case of an anti-reflective multi-layered film, it is necessary to form a film having a low refractive index for the outermost layer facing the side of air as is clear from the construction of the above-mentioned anti-reflective film. Since there is no material for the transparent conductive film which satisfies the property of a low refractive index as required, it is necessary that a transparent conductive film is used for an inner layer and an insulating material having a low refractive index such a MgF.sub.2, SiO.sub.2 or the like is used for the outermost layer.
Various methods have been proposed to produce a panel with an anti-reflective multi-layered film wherein an electric charge produced on the surface of the panel by the electrification is led to the ground through a transparent conductive film which is formed as an inner layer in the anti-reflective-multi-layered film.
An attempt to let an electric charge escape by forming a solder layer on the outermost layer of the anti-reflective film was made. As a result, it was found that the wettability of the outermost layer, e.g. MgF.sub.2 or SiO.sub.2 of the anti-reflective film to the solder layer was not so good, and provision of the solder layer on the outermost layer did not sufficiently function as earthing at a low resistance value because a non-conductive layer was interposed.
An attempt of letting an electric charge escape by directly contacting a plate spring made of metal on the outermost layer of the anti-reflective film was made. However, the resistance between the plate spring and the transparent conductive layer was very high because the outermost layer without electric conductive property was intervened and a complete contacting state of the plate spring could not be obtained, whereby an electric breakdown was caused at a part of the anti-reflective multi-layered film to thereby deteriorate the film.
Further, an attempt of bonding an electric conductive tape comprising a copper foil with an adhesive to the surface of the multi-layered film was made. However, the electric conductivity of the adhesive was not sufficient and an electric breakdown was caused.